Obtaining reliable and specific data for adaptive digital predistortion

ABSTRACT

Systems, devices, and methods related to performing digital predistortion in radio frequency (RF) systems are provided. A digital predistortion (DPD) arrangement includes a DPD actuator circuit to predistort, using DPD coefficients, at least a portion of an input signal, the DPD coefficients associated with a characteristic of a nonlinear component. The DPD arrangement further includes a DPD capture circuit to perform, based on a capture cycle timing, multiple captures of a feedback signal, the feedback signal indicative of an output of the nonlinear component; compute, based on one or more characteristics of the multiple captures, one or more criteria for a subsequent capture of the feedback signal; and perform, based on the one or more criteria, the subsequent capture of the feedback signal. The DPD arrangement circuit further includes a DPD adaptation circuit to update the DPD coefficients based at least in part on the subsequent capture.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. Pat. Application No.17/537,724 entitled “OBTAINING RELIABLE AND SPECIFIC DATA FOR ADAPTIVEDIGITAL PREDISTORTION” and filed Nov. 30, 2021, which claims priority toand the benefit of the U.S. Provisional Patent Application No.63/123,573 entitled “OBTAINING RELIABLE AND SPECIFIC DATA FOR ADAPTIVEDIGITAL PREDISTORTION” and filed Dec. 10, 2020, the disclosures of eachof which are hereby incorporated by reference in their entireties as iffully set forth below and for all applicable purposes.

TECHNICAL FIELD OF THE DISCLOSURE

The present disclosure generally relates to electronics, and, morespecifically, to performing digital predistortion in radio frequency(RF) systems.

BACKGROUND

Radio systems are systems that transmit and receive signals in the formof electromagnetic waves in the RF range of approximately 3 kilohertz(kHz) to 300 gigahertz (GHz). Radio systems are commonly used forwireless communications, with cellular/wireless mobile technology beinga prominent example but may also be used for cable communications suchas cable television. In both of these types of systems, linearity ofvarious components therein plays a crucial role.

Linearity of an RF component or a system such as an RF transceiver iseasy to understand in theory. Namely, linearity generally refers to theability of a component or a system to provide an output signal that isdirectly proportional to an input signal. In other words, if a componentor a system is perfectly linear, the relationship of a ratio of theoutput signal to the input signal is a straight line. Achieving thisbehavior in real-life components and systems is far more complicated andmany challenges to linearity must be resolved, often at the expense ofsome other performance parameter, such as efficiency and/or outputpower.

Made from semiconductor materials, which are inherently nonlinear, andhaving to operate at relatively high power levels, power amplifiers(PAs) are usually the first components to analyze when considering adesign of an RF system in terms of linearity. PA outputs with nonlineardistortions can result in reduced modulation accuracy (e.g., reducederror vector magnitude (EVM)) and/or out-of-band emissions. Therefore,both wireless RF systems (e.g., Long-Term Evolution (LTE) andmillimeter-wave or 5^(th) generation (5G) systems) and cable RF systemshave stringent specifications on PA linearity.

Digital predistortion (DPD) can be applied to enhance linearity of a PA.Typically, DPD involves applying, in the digital domain, predistortionto a signal to be provided as an input to a PA to reduce and/or canceldistortion that is expected to be caused by the PA. The predistortioncan be characterized by a PA model. The PA model can be updated based ona feedback signal from the PA (i.e., based on the output of the PA). Themore accurate a PA model is in terms of predicting the distortions thatthe PA will introduce, the more effective the predistortion of an inputto the PA will be in terms of reducing the effects of the distortioncaused by the amplifier.

Obtaining an accurate PA model that may be used to perform DPD is nottrivial and further improvements would be desirable.

BRIEF DESCRIPTION OF THE DRAWINGS

To provide a more complete understanding of the present disclosure andfeatures and advantages thereof, reference is made to the followingdescription, taken in conjunction with the accompanying figures, whereinlike reference numerals represent like parts, in which:

FIG. 1 illustrates data bursts in an example signal;

FIG. 2 illustrates how charge trapping can affect the gain in an examplesignal;

FIG. 3 illustrates an example signal and a charge trap (CT) model withthe mean gain in each symbol period;

FIG. 4 illustrates a schematic block diagram of a communication systemwith a multi-mode DPD capture circuit, according to some embodiments ofthe present disclosure;

FIG. 5 illustrates a schematic block diagram of a part of acommunication system with a multi-mode DPD capture circuit and capturebuffers, according to some embodiments of the present disclosure;

FIG. 6 provides a schematic block diagram illustrating an RF system inwhich DPD using a multi-mode DPD capture circuit may be implemented,according to some embodiments of the present disclosure;

FIG. 7 provides a block diagram illustrating an example data processingsystem that may be configured to implement, or control, at leastportions of performing DPD using a multi-mode DPD capture circuit,according to some embodiments of the present disclosure;

FIG. 8 is a block diagram illustrating an example DPD capture circuit,according to some embodiments of the present disclosure; and

FIG. 9 is a flow diagram of an example method for capturing data for DPDadaptation, according to some embodiments of the present disclosure.

DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE DISCLOSURE Overview

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for allof the desirable attributes disclosed herein. Details of one or moreimplementations of the subject matter described in this specificationare set forth in the description below and the accompanying drawings.

For purposes of illustrating DPD techniques proposed herein, it might beuseful to first understand phenomena that may come into play incommunication systems. The following foundational information may beviewed as a basis from which the present disclosure may be properlyexplained. Such information is offered for purposes of explanation onlyand, accordingly, should not be construed in any way to limit the broadscope of the present disclosure and its potential applications.

Solid-state devices that can be used in high-frequency applications areof great importance in modern semiconductor technologies. Due, in part,to their large band gap and high mobility, III-N based transistors(i.e., transistors that employ compound semiconductor materials with afirst sub-lattice of at least one element from group III of the periodictable (e.g., Al, Ga, In) and a second sub-lattice of nitrogen (N) aschannel materials), such as gallium nitride (GaN) based transistors, maybe particularly advantageous for high-frequency applications. Inparticular, PAs may be built using GaN transistors.

While GaN transistor have desirable features in terms of cut-offfrequency and efficiency, their behavior is complicated by an effectknown at charge trapping, where defect sites in the transistor channeltrap charge carriers. The density of trapped charges is largelydependent on the gate voltage, where the gate voltage is typicallyproportional to the signal amplitude. To complicate things further, anopposite effect may simultaneously compete with the effect of chargetrapping. Namely, as some charge carriers are trapped by defect sites,other charge carriers are released from the traps, e.g., due to thermalactivation. These two effects have very different time constants: thedefect sites may be filled with trapped charges quickly any time thegate voltage is increased, while the release of trapped charges happensmore slowly. The release time constants can be 10′s of microseconds andup to milliseconds, with the effect typically being very visible on thetime scale of the symbol periods in 4G or 5G data, especially for datathat contains bursts.

FIG. 1 provides an illustration 100, showing an example signal with databursts. The horizontal axis of FIG. 1 indicates data samples of thesignal, while the vertical axis indicates the signal amplitude. LettersA, B, C, D, and E, shown in FIG. 1 , label peaks in various portions ofthe signal. FIG. 2 provides an illustration 200, showing an examplesignal with data bursts similar to that shown in FIG. 1 , but now alsoillustrating how charge trapping can affect the gain in the signal. Inparticular, FIG. 2 shows an amplitude plot of a 4G standard test signal,labeled in FIG. 2 as a signal 202, known at ETM2 in the 3GPP standards.A curve 204, shown in FIG. 2 as an overlay over the amplitude plot ofthe signal 202, illustrates a typical expected behavior for the CTdensity/state. FIG. 2 illustrates that the CT state (i.e., the curve204) rises rapidly every time there is a power burst (i.e., every timethere is a burst in the signal 202 where the amplitude of the signal 202sharply increases) and then decays slowly in the regions where thesignal 202 is of relatively low power. The charge in the traps acts tooppose the effect of the applied gate voltage to the transistor channeland is, thus, manifested macroscopically as a modulation of the gain ofthe transistor. FIG. 3 provides an illustration 300, showing an examplesignal and a CT model with the mean gain in each symbol period. As canbe seen from FIG. 3 , the mean gain varies in different portions of thesignal. It is this dynamic gain change that affects the signal qualityin GaN PAs.

The signal quality is the measure of how closely the amplifier islinear, i.e., of how closely the signal that is transmitted from theoutput of the PA matches the signal that is provided to the input of thePA. The signal 202 shown in FIG. 2 may be seen as an illustration of asignal provided to the input of the PA, while the signal 204 shown inFIG. 2 provides an illustration of how a signal at the output of the PAwould change, compared to the input signal, because of the effectswithin the PA. FIG. 2 illustrates that the relatively fast chargetrapping and the relatively slow charge release in a GaN PA may distortthe input signal to the PA in a nonlinear manner, resulting in adistorted signal at the output of the amplifier.

As described above, DPD can pre-distort an input to a PA to reduceand/or cancel distortion caused by the amplifier. To that end, at a highlevel, DPD involves forming a model of how a PA may affect an inputsignal, the model defining coefficients of a filter, or gain, to beapplied to the input signal in an attempt to reduce and/or cancel thedistortion of the input signal caused by the amplifier. In this manner,DPD will try to compensate for a nonlinear gain of the amplifier, byapplying a corresponding gain to the input signal, where typically onegain is applied at any one signal amplitude.

The model used in DPD algorithms is an adaptive model, meaning that itis formed in an iterative process by gradually adjusting thecoefficients based on the comparison between the data that comes intothe input to the amplifier and the data that comes out from the outputof the amplifier. Estimation of DPD coefficients is based on captures ofa finite sequence of input and output data (i.e., input to and outputfrom a PA).

One aspect of the present disclosure provides a DPD capture unitconfigured to offer multiple configurable modes for capturing feedbacksignals from a PA. Such a DPD capture unit is referred to as a“multi-mode DPD capture circuit.” In mode 1, the peak sample power in acertain window is presented substantially in the center of a capturebuffer. In mode 2, the peak window start may be synchronized with aframe at a programmed offset. In mode 3, data may be decimated prior tocapture. In mode 4, multiple capture cycles may be performed in a quicksuccession (in a “burst mode”) to compute certain statisticalcharacteristics of data. Such capture cycles of samples of a feedbacksignal may be referred to as “trial captures” and each trial capture mayinclude L consecutive samples of the feedback signal. The statisticalcollected characteristics may then be used to set conditions foracquiring non-trial captures (i.e., for performing acquiring thecaptures to be used in updating a PA model). In an operational variationof mode 4, the non-trial captures may be collected. A burst mode may beconfigured as in mode 4 and the burst may be terminated when theconditions set following a mode 4 burst are met in a capture sample. Theconditions that are to be met for the acquisition of the capture may belogical combinations of threshold comparisons on the characteristics ofthe statistics. In mode 5, the samples are accumulated over multiplecaptures in order to perform averaging to reduce noise. Capturescollected by the DPD capture unit may be used to update a PA model,which model may be used to apply digital predistortion to an inputsignal. Having a multi-mode DPD capture circuit offering multipleconfigurable modes allows for combinations of timing and signalcondition selection that can be adapted to the requirements of variousDPD algorithms such that reliable and specific data may be captured forperforming adaptive DPD, thus providing provides for a stable andaccurate estimation of DPD coefficients.

While some of the descriptions are provided herein with reference to GaNbased PAs, in general, various embodiments of the methods of digitalpredistortion with power-specific capture selection presented herein areapplicable to PAs which are not GaN based, as well as to any nonlinearelectronic components (i.e., components that may exhibit nonlinearbehavior) other than PAs.

Various embodiments of performing DPD using a multi-mode DPD capturecircuit are explained herein with reference to the “input signals forPAs” being drive signals for the PAs, i.e., signals generated on thebasis of the input signals x, described herein, to which the DPDarrangement applies predistortion based on the DPD coefficients.However, in other embodiments of DPD using a multi-mode DPD capturecircuit as described herein, the “input signals for PAs” may be biassignals used to bias the PAs. Thus, embodiments of the presentdisclosure include DPD arrangements similar to the ones described hereinand illustrated in the drawings, except that, instead of modifying thedrive signals for the PAs, DPD circuit may be configured to modify thebias signals for the PAs, which may be done based on control signalsgenerated by a DPD adaptation circuit (e.g., the DPD adaptation circuit414, described herein). The output of the PA array is based on the biassignals used to bias the array of PAs individually or collectively. Inother aspects of the present disclosure, both drive signals and biassignals for the PA array may be adjusted as described herein toimplement of DPD using a multi-mode DPD capture circuit as describedherein.

Furthermore, while some of the descriptions are provided herein withreference to PAs, in general, various embodiments of DPD using amulti-mode DPD capture circuit, presented herein, are applicable toamplifiers other than PAs, such as low-noise amplifiers, variable gainamplifiers, etc., as well as to nonlinear electronic components of RFtransceivers (i.e., components that may exhibit nonlinear behavior)other than amplifiers. Furthermore, while some of the descriptions areprovided herein with reference to wireless communication systems ofmillimeter-wave/5G technologies, in general, various embodiments of DPDusing a multi-mode DPD capture circuit, presented herein, are applicableto wireless communication systems of any technology or standard otherthan millimeter-wave/5G, and/or to any wireless RF systems other thanwireless communication systems, and/or to any RF systems other thanwireless systems.

As will be appreciated by one skilled in the art, aspects of the presentdisclosure, in particular aspects of RF transceivers with DPD using amulti-mode DPD capture circuit as described herein, may be embodied invarious manners - e.g. as a method, a system, a computer programproduct, or a computer-readable storage medium. Accordingly, aspects ofthe present disclosure may take the form of an entirely hardwareembodiment, an entirely software embodiment (including firmware,resident software, micro-code, etc.) or an embodiment combining softwareand hardware aspects that may all generally be referred to herein as a“circuit,” “arrangement,” “module,” or “system.” At least some of thefunctions described in this disclosure may be implemented as analgorithm executed by one or more hardware processing units, e.g. one ormore microprocessors, of one or more computers. In various embodiments,different steps, and portions of the steps of any methods describedherein may be performed by different processing units. Furthermore,aspects of the present disclosure may take the form of a computerprogram product embodied in one or more computer-readable medium(s),preferably non-transitory, having computer-readable program codeembodied, e.g., stored, thereon. In various embodiments, such a computerprogram may, for example, be downloaded (updated) to various devices andsystems (e.g. to various components and arrangements of components of RFtransceivers, and/or their controllers, etc.) or be stored uponmanufacturing of these devices and systems.

The following detailed description presents various descriptions ofspecific certain embodiments. However, the innovations described hereincan be embodied in a multitude of different ways, for example, asdefined and covered by the claims or select examples. In the followingdescription, reference is made to the drawings, where like referencenumerals can indicate identical or functionally similar elements. Itwill be understood that elements illustrated in the drawings are notnecessarily drawn to scale. Moreover, it will be understood that certainembodiments can include more elements than illustrated in a drawingand/or a subset of the elements illustrated in a drawing. Further, someembodiments can incorporate any suitable combination of features fromtwo or more drawings.

The description may use the phrases “in an embodiment” or “inembodiments,” which may each refer to one or more of the same ordifferent embodiments. Unless otherwise specified, the use of theordinal adjectives “first,” “second,” and “third,” etc., to describe acommon object, merely indicate that different instances of like objectsare being referred to, and are not intended to imply that the objects sodescribed must be in a given sequence, either temporally, spatially, inranking or in any other manner. Furthermore, for the purposes of thepresent disclosure, the phrase “A and/or B” or notation “A/B” means (A),(B), or (A and B), while the phrase “A, B, and/or C” means (A), (B),(C), (A and B), (A and C), (B and C), or (A, B, and C). As used herein,the notation “A/B/C” means (A, B, and/or C). The term “between,” whenused with reference to measurement ranges, is inclusive of the ends ofthe measurement ranges.

Various aspects of the illustrative embodiments are described usingterms commonly employed by those skilled in the art to convey thesubstance of their work to others skilled in the art. For example, theterm “connected” means a direct electrical connection between the thingsthat are connected, without any intermediary devices/components, whilethe term “coupled” means either a direct electrical connection betweenthe things that are connected, or an indirect connection through one ormore passive or active intermediary devices/components. In anotherexample, the term “circuit” means one or more passive and/or activecomponents that are arranged to cooperate with one another to provide adesired function. Sometimes, in the present descriptions, the term“circuit” may be omitted (e.g., a DPD actuator circuit 412 shown in thepresent drawings may be referred to in the present descriptions as a“DPD actuator 412,” etc.). If used, the terms “substantially,”“approximately,” “about,” etc., may be used to generally refer to beingwithin +/- 20% of a target value, e.g., within +/-10% of a target value,based on the context of a particular value as described herein or asknown in the art.

Example Communication System with a Multi-Mode DPD Capture Circuit

As summarized above, embodiments of the present disclosure relate toperforming DPD with capture acquisition performed by a multi-mode DPDcapture circuit. To that end, a system as shown in FIG. 4 may be used.

FIG. 4 illustrates a schematic block diagram of a communication system400 with a DPD circuit 410 configured to implement multi-mode captureacquisition, according to some embodiments of the present disclosure.FIG. 4 illustrates that the communication system 400 may include atransmitter circuit (or, simply, a “transmitter”) 420 in communicationwith the DPD circuit 410, and a PA 430 in communication with thetransmitter 420. The output from the PA may be provided, as a feedbacksignal, to a receiver circuit (or, simply, a “receiver”) 440 that isalso in communication with the DPD circuit 410.

As shown in FIG. 4 , the DPD circuit 410 may include a DPD actuator 412,an adaptation circuit 414, and a multi-mode DPD capture circuit 416. Thetransmitter 420 may include a digital filter 422, a digital-to-analogconverter (DAC) 424, an analog filter 426, and a mixer 428. The receiver440 may include a digital filter 442, an analog-to-digital converter(ADC) 444, an analog filter 446, and a mixer 448. In variousembodiments, the communications system 400 can include fewer or moreelements than those illustrated in FIG. 4 .

An input signal X (labeled in FIG. 4 as _(Xn), referring to a sequenceof digital samples of the signal X) may be received by the DPD actuator412. In some embodiments, the input signal X may include one or moreactive channels in the frequency domain. In some embodiments, the inputsignal X may be a baseband digital signal. The DPD actuator 412 may beconfigured to pre-distort the input signal X based on predistortioncoefficients α provided by the DPD adaptation circuit 414. In turn, theDPD adaptation circuit 414 may be configured to generate thepredistortion coefficients based on a model that the DPD adaptationcircuit 414 updates based on captures acquired by the multi-mode DPDcapture circuit 416, described in greater detail below. The DPD actuator412 can provide the predistorted input Y (labeled in FIG. 4 as y_(n),referring to a sequence of digital samples of the signal Y), which isthe input signal X to which predistortion has been applied, to thetransmitter 420. The DPD actuator 412 can be implemented by any suitablecircuits. For instance, in some embodiments, the DPD actuator 412 can beimplemented by combinational logic circuits.

It should be noted that, while a differentiation between the adaptationcircuit 414 and the multi-mode DPD capture circuit 416 is made in theillustration of these circuits in the drawings and in the descriptionsof these circuits, this differentiation may be only logical, todifferentiate functions that may be performed by a conventional DPDcircuit (described herein with reference to the adaptation circuit 414)and functions specifically related to multi-mode capture selection(described herein with reference to the multi-mode DPD capture circuit416). In various embodiments, functionality of the multi-mode DPDcapture circuit 416 may be included in, or be considered as a part of,the adaptation circuit 414, or functionalities of these two circuits maybe spread over a larger number of individual circuits.

The transmitter 420 may be configured to upconvert the predistortedinput Y from a baseband signal to a higher frequency signal, such as anRF signal. In the illustrated transmitter 420, the predistorted input Ymay be filtered in the digital domain by the digital filter 422 togenerate a filtered predistorted input Y, a digital signal. The outputof the digital filter 422 may then be converted to an analog signal bythe DAC 424. The analog signal provided by the DAC 424 may then befiltered by an analog filter 426. The output of the analog filter 426may then be upconverted to RF by the mixer 428, which may receive asignal from a local oscillator 450 to translate the filtered analogsignal from the analog filter 426 from baseband to RF. Other methods ofimplementing the transmitter 420 are also possible and within the scopeof the present disclosure. For instance, in another implementation (notillustrated) the output of the digital filter 422 can be directlyconverted to an RF signal by the DAC 424. In such an implementation, theRF signal provided by the DAC 424 can then be filtered by the analogfilter 426. Since the DAC 424 would directly synthesize the RF signal inthis implementation, the mixer 428 and the local oscillator 450illustrated in FIG. 4 can be omitted from the system 400 in suchembodiments.

As further illustrated in FIG. 4 , the RF signal generated by thetransmitter 420 is provided to the PA 430. The PA 430 amplifies the RFsignal and provides an amplified RF signal Z (labeled in FIG. 4 asz_(n), referring to a sequence of analog values of the signal Z). Theamplified RF signal Z can be provided to an antenna (not illustrated inFIG. 4 ) to be wirelessly transmitted. The amplified RF signal Z has asignal bandwidth. The signal bandwidth can be a wide bandwidth. As onenon-limiting example, the signal bandwidth can be about 1 GHz. Theamplified RF signal Z is an amplified version of the input signal X.However, as discussed above, the amplified RF signal Z can havedistortions outside of the main signal components. Such distortions canresult from nonlinearities in the response of the PA 430. As discussedabove, it can be desirable to reduce such nonlinearities. Accordingly,feedback from the output of the PA 430 can be provided to the DPDcircuit 410 by way of the receiver 440. The DPD circuit 410 can use thefeedback from the PA 430 to adjust the predistortion applied to theinput signal X to reduce the nonlinearities in the response of the PA430.

To provide feedback to the DPD circuit 410, at least a portion 431 ofthe amplified RF signal Z can be provided to the receiver 440. Forexample, in some embodiments, a feedback element (not illustrated) maybe used in the signal path between the output of the PA 430 and thereceiver 440, e.g., a resistive element that feeds back a relativelysmall portion of the amplified RF signal to the receiver 440. In someother embodiments (also not illustrated), a directional coupler or othersuitable circuit can provide a portion of the amplified RF signal Z tothe receiver 440. In some embodiments (not illustrated), a feedbackfilter may be provided in the signal path between the output of the PA430 and the receiver 440, e.g., to filter the feedback signal 431 andprovide the filtered signal as a feedback signal to the receiver 440 forprocessing. The feedback signal 431 provided to the receiver 440 canhave approximately the same bandwidth as the amplified RF signal Z.

In some embodiments, the receiver 440 is configured to performdiagnostics and/or equalization. Accordingly, the receiver 440 can beutilized for providing feedback to the DPD circuit 410 and fordiagnostics and/or equalization in such embodiments. In the illustratedreceiver 440, the feedback signal 431 may be downconverted to thebaseband by the mixer 448, which may receive a signal from a localoscillator 460 (which may be the same or different from the localoscillator 450) to translate the feedback signal 431 from the RF to thebaseband. The output of the mixer 448 may then be filtered by the analogfilter 446. The output of the analog filter 446 may then be converted toa digital signal by the ADC 444. The digital signal generated by the ADC444 may then be filtered in the digital domain by the digital filter 442to generate a filtered downconverted digital feedback signal 441 whichmay be provided to the DPD circuit 410. Other methods of implementingthe receiver 440 are also possible and within the scope of the presentdisclosure. For instance, in another implementation (not illustrated)the RF feedback signal 431 can be directly converted to a basebandsignal by the ADC 444. In such an implementation, the downconvertedsignal provided by the ADC 444 can then be filtered by the digitalfilter 442. Since the ADC 444 would directly synthesize the basebandsignal in this implementation, the mixer 448 and the local oscillator460 illustrated in FIG. 4 can be omitted from the system 400 in suchembodiments.

Further variations are possible to the system 400, described above. Forexample, while upconversion and downconversion is described with respectto the baseband frequency, in other embodiments of the system 400, anintermediate frequency (IF) may be used instead. IF may be used insuperheterodyne radio receivers, in which a received RF signal isshifted to an IF, before the final detection of the information in thereceived signal is done. Conversion to an IF may be useful for severalreasons. For example, when several stages of filters are used, they canall be set to a fixed frequency, which makes them easier to build and totune. In some embodiments, the mixers of RF transmitter 420 or thereceiver 440 may include several such stages of IF conversion. Inanother example, although a single path mixer is shown in each of thetransmit (TX) path (i.e., the signal path for the signal to be processedby the transmitter 420) and the receive (RX) path (i.e., the signal pathfor the signal to be processed by the receiver 440) of FIG. 4 , in someembodiments, the TX path mixer 428 and the RX path mixer 448 may beimplemented as a quadrature upconverter and downconverter, respectively,in which case each of them would include a first mixer and a secondmixer. For example, for the RX path mixer 448, the first RX path mixermay be configured for performing downconversion to generate an in-phase(I) downconverted RX signal by mixing the feedback signal 431 and anin-phase component of the local oscillator signal provided by the localoscillator 460. The second RX path mixer may be configured forperforming downconversion to generate a quadrature (Q) downconverted RXsignal by mixing the feedback signal 431 and a quadrature component ofthe local oscillator signal provided by the local oscillator 460 (thequadrature component is a component that is offset, in phase, from thein-phase component of the local oscillator signal by 90 degrees). Theoutput of the first RX path mixer may be provided to a I-signal path,and the output of the second RX path mixer may be provided to a Q-signalpath, which may be substantially 90 degrees out of phase with theI-signal path.

Obtaining Reliable and Specific Data Using a Multi-Mode DPD CaptureCircuit

Turning to the details of the DPD circuit 410, functionality ofperforming DPD using a multi-mode DPD capture circuit according tovarious embodiments of the present disclosure may be illustrated withreference to FIG. 5 , providing a schematic illustration of a part of acommunication system 500, e.g., a part of the communication system 400,that includes the multi-mode DPD capture circuit 416 and capture buffers502.

In some embodiments, the multi-mode DPD capture circuit 416 may be ahardware unit that includes suitable memory (e.g., random-access memory(RAM)) and supporting arithmetic and logic functions. In someembodiments, the multi-mode DPD capture circuit 416 may include at leastportions of a data processing system as shown in FIG. 7 . The multi-modeDPD capture circuit 416 may be configured to capture data for use in DPDestimation of DPD coefficients from selectable nodes in a radiotransceiver device, e.g., in a device as shown in FIG. 4 and/or a deviceas shown in FIG. 6 . The multi-mode DPD capture circuit 416 has multipleconfigurable modes that allow for combinations of timing and signalcondition selection that can be adapted to the requirements of variousDPD algorithms such that the data collected provides for a stable andaccurate estimation.

In cellular radio standards the radio transmission is normally dividedinto frames, typically of 10 milliseconds (ms) duration. Each frame maythen be divided into subframes, timeslots, and symbols. For example, a4G frequency domain duplex (FDD) frame typically includes 10 subframes,each subframe including 14 symbol periods. Although the data beingtransmitted by a communication system is dynamic, there is, for the mostpart, similarity between successive frames. Ideally, DPD should sampleone or more frames in their entirety for an accurate model, but foreconomy of complexity, DPD estimation must be based on data samples of aduration that is shorter than an entire frame. Therefore, carefullyselecting portions of a feedback signal from which captures will beacquired for DPD estimation is important to ensure performance andstability. Embodiments of the present disclosure are based onrecognition that a variety of signal conditions and performance targetsare to be accounted for in selecting captures to be used by the DPDadaptation circuit 414 for DPD estimation.

The major blocks of an adaptive DPD system are shown in FIG. 5 . In theillustration of FIG. 5 , analog conversion functions are implicit, soeach data line represents digital signals. The capture buffers 502 maybe configured to store samples of two or more of the digital signalsshown. For example, the capture buffers 502 may store samples of theinput signal X and of the feedback signal 431 (Z). The data pointsstored in the capture buffers 502 may depend on the DPD modelimplemented by the DPD adaptation circuit 414 to compute the DPDcoefficients. Because of the high sample rate of the signals to bestored in the capture buffers 502 and, hence, the cost of the memoryunit used to implement the capture buffers 502 (e.g., RAM), each bufferof the capture buffers 502 may be limited in size, e.g., limited tobeing 4 kilobytes (Kbytes) or 8 Kbytes deep. Therefore, the time span ofa capture can be only on the order of tens of microseconds (us) out ofthe entire duration of a frame. However multiple captures, e.g., 4 or 8captures, may be taken and aggregated for one DPD estimation.

Embodiments of the present disclosure covers a design of a multi-modeDPD capture circuit 416 that has multiple modes that support differentobjectives. The modes and the rationale for each mode are describedbelow. While 5 modes are described, in various embodiments, themulti-mode DPD capture circuit 416 may be configured to implement anycombination of 2 or more of these modes.

In mode 1, which may be referred to as a “centering mode,” themulti-mode DPD capture circuit 416 may be configured to present the peaksample power in a certain window substantially in the center of acapture buffer. The DPD estimation process is in part a curve-fittingexercise. In order to prevent extrapolation which may lead toinaccuracy, the sampled data should include the peak power to beexpected for the lifetime of the estimation. The best guess at this isthe highest peaks that have occurred in recent history. In mode 1, themulti-mode DPD capture circuit 416 may be configured to detect thehighest peak occurring in a programmable time window (which may bereferred to as a “peak search window”) and center the peak in the middleof the capture buffer 502. In some embodiments, this may be implementedby the multi-mode DPD capture circuit 416 analyzing a certain window ofdata samples of the feedback signal 441, identifying the peak powervalue within that window of data samples, and creating an initializationsignal for a capture buffer address counter that enables writingsuccessive samples to the buffer. In some embodiments, a delay lineequal to about half the buffer size may be inserted in the signal pathso that the peak power sample is centered. As a result of thisoperation, the peak power value will be substantially in the center ofthe capture buffer. Presenting the peak sample power substantially inthe center of a capture buffer may be advantageous in terms of ensuringthat the capture used for DPD estimation contains the signal peak andits side lobes so that the model estimated by the DPD function containsthe optimal representation of the signal statistics in the vicinity ofthe peak, which may be desirable for precise and stable behavior. In adynamic signal environment, the frequency content of the signal canvary. When this frequency content is such that the signal has a narrowbandwidth, the signal is spread out in the time domain. A peak in anarrow-bandwidth signal will have a wide main lobe and side lobes thatextend out, so that centering the peak advantageously allows to collectas much of the signal’s content as is possible in a capture of a finitelength.

In mode 2, which may be referred to as a “frame synchronization mode,”the multi-mode DPD capture circuit 416 may be configured to synchronizethe start of a peak search window with a frame at a predefinedprogrammable offset with respect to a certain trigger. In someembodiments, the trigger may be a synchronization signal indicating thata new frame starts. In other embodiments, the trigger may be based on acounter, e.g., a particular counter value being reached. In still otherembodiments, the trigger may be based on a certain characteristic of afeedback signal being analyzed meeting predefined criteria (e.g., a peakpower value reaching a predefined threshold). In some embodiments, theframe synchronization mode may include the multi-mode DPD capturecircuit 416 starting a plurality of peak search windows with a frame atdifferent time offsets with respect to one or more triggers. Forexample, in some embodiments of operating in mode 2, the multi-mode DPDcapture circuit 416 may be configured to take multiple captures over thespan of a radio frame, where the multiple captures may be timed withpredefined programmable time offsets from the frame boundary (e.g., timeoffsets with respect to a synchronization signal indicating the start ofa frame). Starting a capture at a predefined programmable time offsetfrom the frame boundary has been used in conventional DPDimplementations. In contrast to such implementations, in mode 2 themulti-mode DPD capture circuit 416 is configured to start the peaksearch window after such a predefined time offset (i.e., the multi-modeDPD capture circuit 416 may start searching for a peak after such apredefined time offset) and the capture will occur whenever the peak isfound, e.g., centering the peak that was found substantially in thecenter of the capture, as described above. Thus, when operating in mode2, the multi-mode DPD capture circuit 416 is configured to start a peaksearch window at a predefined programmable time offset from a frameboundary, but the capture itself may happen at a later point in time,depending on the data in the peak search window. This can also be donein combination with mode 1 so that at the predetermined frame time apeak search window is initiated. For example, taking 5 captures withwindows of 2 ms each spaced by 2 ms apart will obtain 5 captures thatinclude the peaks in 5 different frame regions. Such captures (with thecycle timing of 2 ms on and 2 ms off for 5 cycles of data capturing) mayhave different frequency and/or power content, enabling the multi-modeDPD capture circuit 416 to assemble a more fully representative datasample. The timed peak window captures can also be used to estimatedifferent models for different sections of the frame in order tocompensate for transient effects, for example at the onset of thetransmit periods in time-domain duplex (TDD) frames.

In mode 3, which may be referred to as a “decimation mode,” themulti-mode DPD capture circuit 416 may be configured to performdecimation/downsampling of data prior to capture, where the term“decimation” refers to the process of reducing the sampling rate. Inorder to model long-term effects such as charge trapping and thermalmemory, larger time spans must be represented in the capture set.Because the capture buffers 502 are limited to a certain number ofsamples that they may store, representing larger time spans may berealized by the multi-mode DPD capture circuit 416 decimating the databefore storing the data in the capture buffers 502. For example, for a10mS frame LTE signal, it may be desirable to use a capture of a timespan of 1 ms in order to represent relatively long-term effects such ascharge trapping and thermal memory. For a 500 MHz sample rate, thiswould mean that 500,000 samples need to be stored in the capture buffers502. However, each of the capture buffers 502 may only be, e.g., 8Kbytes deep, which is too little to store all of the desired data. Byperforming decimation at a rate of 64, the number of samples could bereduced to about 7.8 K (500,000/64=7,812.5) samples which would allowstoring samples covering the desired time span in one of the capturebuffers 502. In some conventional implementations, a digitized feedbacksignal is decimated in order to set the capture buffer to a fixed samplerate, namely that of the DPD actuator. In contrast to suchimplementations, in the decimation mode, the multi-mode DPD capturecircuit 416 is configured to decimate not only the digitized feedbacksignal 441 but also the input signal X. In some embodiments, the samplerate of the DPD estimation to be adapted during live operation. In someembodiments, DPD actuator arrangements that include multiple actuatorsoperating at difference sample rates can be constructed, which alloweffects over both short- and long-time scales to be corrected. Thedecimation mode allows each of these actuators to be estimated using thesame capture buffers circuits. Furthermore, in some embodiments,operation of the multi-mode DPD capture circuit 416 in mode 3 may becombined with operation in mode 2 so that different sections of theframe can be sampled to provide a more complete model of the variationin long-term behavior within the signal.

In mode 4, which may be referred to as a “burst mode,” the multi-modeDPD capture circuit 416 may be configured to perform multiple capturecycles with specified timing to collect statistics of trial captures sothat the multi-mode DPD capture circuit 416 or the DPD adaptationcircuit 414 may use the collected statistics to set criteria foracquiring targeted captures, e.g., by setting thresholds for non-trialcaptures based on the collected statistics. For example, in someembodiments, the statistics may include one or more of peak power abovea programmable threshold (an upper bound threshold peak power) in therange zero to maximum power, peak power below a programmable threshold(a lower bound threshold peak power) in the range zero to maximum power,mean power above a programmable threshold (an upper bound threshold meanpower) in the range zero to maximum power, mean power below aprogrammable threshold (a lower bound threshold mean power) in the rangezero to maximum power, number of samples of power exceeding aprogrammable threshold (an upper bound threshold number of samples)greater than another programmable threshold, number of samples of powerexceeding a programmable threshold (a lower bound threshold number ofsamples) less than another programmable threshold, and so on. In someembodiments of the burst mode, the multi-mode DPD capture circuit 416may be configured to repeat capture until a logical combination ofthreshold comparisons is true. Phrased differently, some embodiments ofthe burst mode may be seen as the multi-mode DPD capture circuit 416being configured to keep “looking” at (monitoring) the feedback signal,without storing any captures, until some logical combination of one ormore thresholds is true, and then is configured to start capturing(i.e., storing samples of the capture) when the logical combination ofone or more thresholds becomes true (e.g., it could be implemented asmode 3 except that the WRITE operation to the capture buffer is enabledfor mode 3 and disabled for the burst mode). The burst mode allows forstatistics of expected captures to be obtained which are then used toset the thresholds for a capture targeted to a specific characteristic.Peak power, mean power and number of samples exceeding (or being below)some thresholds are possible measurements. For example, capturesselected by peak power alone may be particularly advantageous for burstysignals with GaN PAs where the charge trapping is highly dependent onlocal peak power and DPD function may be weighted to allow for thevariations along the frame. In another case mean power may be importantwhen considering fast thermal effects. The number of samples over athreshold to exceed a specified amount may be useful to avoid weightingwith zero- or low-power samples where signals include short lengthpulses. The various threshold tests can be combined to increase theprobability of obtaining a reliable capture. The captures acquired inthe burst mode may be referred to as “trial” to indicate that they areused to establish criteria (e.g., thresholds) for when non-trialcaptures are to be acquired from the feedback signal that is indicativeof the output of the PA 430, and to indicate that these burst modecaptures may or may not be used as captures based on which predistortioncoefficients are computed later on. The signal output by the PA 430 maybe an unknown and dynamic signal, in which case the criteria (e.g.,thresholds) for when non-trial captures are to be acquired may need tobe established at the beginning of operation of the system 400, and/orrepeated intermittently. In some embodiments, each trial capture mayinclude L consecutive samples of the digital feedback signal, while, inother embodiments, different trial captures may include different numberof consecutive samples of the digital feedback signal. Stateddifferently, each trial capture may be acquired according to a capturecycle timing, for example, including on/off periods where each on periodmay correspond to the time for acquiring L consecutive samples followedby an off period, or alternatively, each on period may correspond to thetime for acquiring a respective number of consecutive samples followedby an off period. In some embodiments, the multi-mode DPD capturecircuit 416 may include an instantaneous power circuit configured tocompute an instantaneous power of the acquired trial captures. Next,based on the computed instantaneous power, a peak location circuit ofthe multi-mode DPD capture circuit 416 may be configured to identify thehighest peak in the instantaneous power signal for each of the trialcaptures. The instantaneous power of the highest peak of a given trialcapture may then be labeled as the maximum power for the capture, andstored in memory (e.g., in memory described with reference to FIG. 7 ).In some embodiments, the criteria (e.g., thresholds) for when non-trialcaptures are to be acquired may be re-evaluated (i.e., re-established)during operation of the communication system 400 at some desired pointsin time, e.g., periodically, or when the DPD circuit 410 is triggered todo so. In some instances, the instantaneous power circuit and/or thepeak location circuity may be generally referred to as a measurementcircuit.

In some embodiments, operation of the multi-mode DPD capture circuit 416in mode 4 may be combined with operation in mode 1 so that the acquiredstatistics pertain to captures with peak centered. Furthermore, in someembodiments, operation of the multi-mode DPD capture circuit 416 in mode4 may be combined with operation in mode 2 so that the acquiredstatistics pertain to captures in specific parts of the frame (e.g.,specific parts of a radio frame or specific subframes within a radioframe). In other words, the capture cycle timing may be specified (e.g.,configured or programmed) such that captures are in specific parts ofthe frame. Still further, in some embodiments, operation of themulti-mode DPD capture circuit 416 in mode 4 may be combined withoperation in mode 3 so that the acquired statistics pertain to decimatedcaptures in specific parts of the frame.

In mode 5, which may be referred to as an “accumulation mode,” themulti-mode DPD capture circuit 416 may be configured to accumulatesamples are accumulated over multiple captures, e.g., in order toperform averaging to reduce noise. In this mode, the multi-mode DPDcapture circuit 416 may be configured to capture repeated transmissionsand accumulate these captures in order to average-out noise. In someembodiments, this mode may be used for pilot symbols and for somespecial measurement that involve a low energy calibration signal. Forexample, if the multi-mode DPD capture circuit 416 is configured tostart a capture of L consecutive data samples of the digitized feedbacksignal 441 at a certain predefined offset with respect to a frameboundary (e.g., as indicated by a synchronization signal), then themulti-mode DPD capture circuit 416 operating in the accumulation modewould first accumulate a plurality of such captures, for differentframes, then combine the plurality of captures in some suitable manner(e.g., by averaging the values of data samples which are in the samelocations within the multiple captures) to generate an accumulatedcapture set of L data samples. In a more specific example, consider thatthe multi-mode DPD capture circuit 416 is configured to start a captureof 4000 consecutive samples starting at a time that is 20% of the totalduration of a frame, as measured from the synchronization signal. Themulti-mode DPD capture circuit 416 may acquire such captures for 5different frames (which may, but do not have to be, consecutive frames)and store the captures in 5 different capture buffers. Then themulti-mode DPD capture circuit 416 may generate sample values for aso-called “accumulated capture buffer” by combining the respectivesample values from these captures of different frames: e.g., the firstsample value of the accumulated capture buffer may be an average of thefirst sample values of the 5 different capture buffers for the differentframes, the second sample value of the accumulated capture buffer may bean average of the second sample values of the 5 different capturebuffers for the different frames, and so on (a combination value otherthan the “average” may be used in different embodiments). It is then thevalues of the accumulated capture buffer that will be used by theadaptation circuit 414 to update the model.

In some embodiments, in each of the capture modes, the multi-mode DPDcapture circuit 416 may be configured and armed for a single or burstcapture by a register-write from a processor subsystem (PS) (where thePS may be implemented in one or more of a processor 2302 shown in FIG. 7, a digital processing unit 2208 shown in FIG. 6 , or a control logic2236 shown in FIG. 6 ). When armed, the multi-mode DPD capture circuit416 may be configured to initiate a single capture or a burst ofcaptures from a trigger which can be provided by a register-write fromthe PS or a signal from an external timing unit. In some embodiments,after the multi-mode DPD capture circuit 416 was operated in the burstmode, the collected statistics may be available in a memory accessed bythe PS. In some embodiments, the multi-mode DPD capture circuit 416 maybe configured to initiate a memory transfer (e.g., by a direct-memoryaccess (DMA) transfer) to the memory of the PS after each capture iscompleted. In some embodiments, the multi-mode DPD capture circuit 416may be configured to assert an interrupt to the PS after each capture iscompleted.

Once the multi-mode DPD capture circuit 416 acquired one or morecaptures in any of the modes described herein, the adaptation circuit414 may use the data samples of the acquired captures to update a modelof the nonlinear electronic component based on one or more of thesecaptures. As a result of updating the model, DPD coefficients may beupdated and provided from the adaptation circuit 414 to the DPD actuator412. Then the DPD actuator 412 may apply the DPD coefficients to realizea predistortion of at least a portion of the input signal X, and thenprovide the predistorted input signal Y to the PA 430. The model formedby the adaptation circuit 414 and the predistortion applied by the DPDactuator 412 may be realized using any suitable conventional DPDalgorithms, or portions thereof, but now using captures obtained asdescribed with reference to the functionality of the multi-mode DPDcapture circuit 416. The consequence of this is that the (single)estimated gain curve may now be a closer fit on average to dynamiccharacter to the signal and more robust to variations and the evolutionof the DPD function, compared to conventional implementations of DPDcaptures. In this manner, the DPD circuit 410 may pre-emptively correct,in the digital domain, for distortions due to the nonlinearity of the PA430 (which, essentially, shapes the input signal X before it gets to thePA 430 to counteract the nonlinearity distortions the PA 430 willproduce). Since the nonlinear gain compression of the PA 430 may varyover time and operating conditions, the feedback loop from the PA 430 tothe receiver 440 and to the DPD circuit 410 can be used to monitor anoutput of the PA 430 and adapt the model accordingly (i.e., to modify orvary the predistortion applied by the DPD actuator 412).

Example RF Devices and Systems

In some embodiments, DPD using a multi-mode DPD capture circuit asdescribed herein may be included in various RF devices and systems usedin wireless communications. For illustration purposes only. One exampleRF device that may include any of the DPD arrangements described hereinis shown in FIG. 6 and described below. However, in general, DPD using amulti-mode DPD capture circuit as described herein may be included insystems other than radio communications, such as in acoustic systems,sonar imaging, or any other systems where beamforming is used and wheresome components may exhibit nonlinear behavior, all of which beingwithin the scope of the present disclosure.

FIG. 6 is a block diagram of an example RF device 2200, e.g., an RFtransceiver, in which DPD using a multi-mode DPD capture circuit asdescribed herein may be implemented, according to some embodiments ofthe present disclosure.

In general, the RF device 2200 may be any device or system that maysupport wireless transmission and/or reception of signals in the form ofelectromagnetic waves in the RF range of approximately 3 kilohertz (kHz)to approximately 300 Gigahertz (GHz). In some embodiments, the RF device2200 may be used for wireless communications, e.g., in a base station(BS) or a user equipment (UE) device of any suitable cellular wirelesscommunications technology, such as GSM, WCDMA, or LTE. In a furtherexample, the RF device 2200 may be used as, or in, e.g., a BS or a UEdevice of a millimeter-wave wireless technology such as fifth generation(5G) wireless (i.e., high-frequency/short-wavelength spectrum, e.g.,with frequencies in the range between about 20 and 60 GHz, correspondingto wavelengths in the range between about 5 and 15 millimeters). In yetanother example, the RF device 2200 may be used for wirelesscommunications using Wi-Fi technology (e.g., a frequency band of 2.4GHz, corresponding to a wavelength of about 12 cm, or a frequency bandof 5.8 GHz, spectrum, corresponding to a wavelength of about 5 cm),e.g., in a Wi-Fi-enabled device such as a desktop, a laptop, a videogame console, a smart phone, a tablet, a smart TV, a digital audioplayer, a car, a printer, etc. In some implementations, a Wi-Fi-enableddevice may, e.g., be a node in a smart system configured to communicatedata with other nodes, e.g., a smart sensor. Still in another example,the RF device 2200 may be used for wireless communications usingBluetooth technology (e.g., a frequency band from about 2.4 to about2.485 GHz, corresponding to a wavelength of about 12 cm). In otherembodiments, the RF device 2200 may be used for transmitting and/orreceiving RF signals for purposes other than communication, e.g., in anautomotive radar system, or in medical applications such as MRI.

In various embodiments, the RF device 2200 may be included in FDD or TDDvariants of frequency allocations that may be used in a cellularnetwork. In an FDD system, the uplink (i.e., RF signals transmitted fromthe UE devices to a BS) and the downlink (i.e., RF signals transmittedfrom the BS to the US devices) may use separate frequency bands at thesame time. In a TDD system, the uplink and the downlink may use the samefrequencies but at different times.

Several components are illustrated in FIG. 6 as included in the RFdevice 2200, but any one or more of these components may be omitted orduplicated, as suitable for the application. For example, in someembodiments, the RF device 2200 may be an RF device supporting both ofwireless transmission and reception of RF signals (e.g., an RFtransceiver), in which case it may include both the components of whatis referred to herein as a transmit (TX) path and the components of whatis referred to herein as a receive (RX) path. However, in otherembodiments, the RF device 2200 may be an RF device supporting onlywireless reception (e.g., an RF receiver), in which case it may includethe components of the RX path, but not the components of the TX path; orthe RF device 2200 may be an RF device supporting only wirelesstransmission (e.g., an RF transmitter), in which case it may include thecomponents of the TX path, but not the components of the RX path.

In some embodiments, some or all the components included in the RFdevice 2200 may be attached to one or more motherboards. In someembodiments, some or all these components are fabricated on a singledie, e.g., on a single system on chip (SOC) die.

Additionally, in various embodiments, the RF device 2200 may not includeone or more of the components illustrated in FIG. 6 , but the RF device2200 may include interface circuitry for coupling to the one or morecomponents. For example, the RF device 2200 may not include an antenna2202, but may include antenna interface circuitry (e.g., a matchingcircuitry, a connector and driver circuitry) to which an antenna 2202may be coupled. In another set of examples, the RF device 2200 may notinclude a digital processing unit 2208 or a local oscillator 2206, butmay include device interface circuitry (e.g., connectors and supportingcircuitry) to which a digital processing unit 2208 or a local oscillator2206 may be coupled.

As shown in FIG. 6 , the RF device 2200 may include an antenna 2202, aduplexer 2204 (e.g., if the RF device 2200 is an FDD RF device;otherwise the duplexer 2204 may be omitted), a local oscillator 2206, adigital processing unit 2208. As also shown in FIG. 6 , the RF device2200 may include an RX path that may include an RX path amplifier 2212,an RX path pre-mix filter 2214, a RX path mixer 2216, an RX pathpost-mix filter 2218, and an ADC 2220. As further shown in FIG. 6 , theRF device 2200 may include a TX path that may include a TX pathamplifier 2222, a TX path post-mix filter 2224, a TX path mixer 2226, aTX path pre-mix filter 2228, and a DAC 2230. Still further, the RFdevice 2200 may further include an impedance tuner 2232, an RF switch2234, and control logic 2236. In various embodiments, the RF device 2200may include multiple instances of any of the components shown in FIG. 6. In some embodiments, the RX path amplifier 2212, the TX path amplifier2222, the duplexer 2204, and the RF switch 2234 may be considered toform, or be a part of, an RF front-end (FE) of the RF device 2200. Insome embodiments, the RX path amplifier 2212, the TX path amplifier2222, the duplexer 2204, and the RF switch 2234 may be considered toform, or be a part of, an RF FE of the RF device 2200. In someembodiments, the RX path mixer 2216 and the TX path mixer 2226 (possiblywith their associated pre-mix and post-mix filters shown in FIG. 6 ) maybe considered to form, or be a part of, an RF transceiver of the RFdevice 2200 (or of an RF receiver or an RF transmitter if only RX pathor TX path components, respectively, are included in the RF device2200). In some embodiments, the RF device 2200 may further include oneor more control logic elements/circuits, shown in FIG. 6 as controllogic 2236, e.g., an RF FE control interface. In some embodiments, thecontrol logic 2236 may be configured to control at least portions ofperforming DPD using data captures by a multi-mode DPD capture circuit,as described herein, e.g., to help linearize the TX path amplifier 2222of the RF device 2200 when the TX path amplifier 2222 includes an arrayof PAs, e.g., an array of PAs similar to the PA 430 as described herein.In some embodiments, the control logic 2236 may be used to performcontrol other functions within the RF device 2200, e.g., enhance controlof complex RF system environment, support implementation of envelopetracking techniques, reduce dissipated power, etc.

The antenna 2202 may be configured to wirelessly transmit and/or receiveRF signals in accordance with any wireless standards or protocols, e.g.,Wi-Fi, LTE, or GSM, as well as any other wireless protocols that aredesignated as 3G, 4G, 5G, and beyond. If the RF device 2200 is an FDDtransceiver, the antenna 2202 may be configured for concurrent receptionand transmission of communication signals in separate, i.e.,non-overlapping and non-continuous, bands of frequencies, e.g., in bandshaving a separation of, e.g., 20 MHz from one another. If the RF device2200 is a TDD transceiver, the antenna 2202 may be configured forsequential reception and transmission of communication signals in bandsof frequencies that may be the same or overlapping for TX and RX paths.In some embodiments, the RF device 2200 may be a multi-band RF device,in which case the antenna 2202 may be configured for concurrentreception of signals having multiple RF components in separate frequencybands and/or configured for concurrent transmission of signals havingmultiple RF components in separate frequency bands. In such embodiments,the antenna 2202 may be a single wide-band antenna or a plurality ofband-specific antennas (i.e., a plurality of antennas each configured toreceive and/or transmit signals in a specific band of frequencies). Invarious embodiments, the antenna 2202 may include a plurality of antennaelements, e.g., a plurality of antenna elements forming a phased antennaarray (i.e., a communication system or an array of antennas that may usea plurality of antenna elements and phase shifting to transmit andreceive RF signals). Compared to a single-antenna system, a phasedantenna array may offer advantages such as increased gain, ability ofdirectional steering, and simultaneous communication. In someembodiments, the RF device 2200 may include more than one antenna 2202to implement antenna diversity. In some such embodiments, the RF switch2234 may be deployed to switch between different antennas.

An output of the antenna 2202 may be coupled to the input of theduplexer 2204. The duplexer 2204 may be any suitable componentconfigured for filtering multiple signals to allow for bidirectionalcommunication over a single path between the duplexer 2204 and theantenna 2202. The duplexer 2204 may be configured for providing RXsignals to the RX path of the RF device 2200 and for receiving TXsignals from the TX path of the RF device 2200.

The RF device 2200 may include one or more local oscillators 2206,configured to provide local oscillator signals that may be used fordownconversion of the RF signals received by the antenna 2202 and/orupconversion of the signals to be transmitted by the antenna 2202.

The RF device 2200 may include the digital processing unit 2208, whichmay include one or more processing devices. The digital processing unit2208 may be configured to perform various functions related to digitalprocessing of the RX and/or TX signals. Examples of such functionsinclude, but are not limited to, decimation/downsampling, errorcorrection, digital downconversion or upconversion, DC offsetcancellation, automatic gain control, etc. Although not shown in FIG. 6, in some embodiments, the RF device 2200 may further include a memorydevice, configured to cooperate with the digital processing unit 2208.

Turning to the details of the RX path that may be included in the RFdevice 2200, the RX path amplifier 2212 may include a low-noiseamplifier (LNA). An input of the RX path amplifier 2212 may be coupledto an antenna port (not shown) of the antenna 2202, e.g., via theduplexer 2204. The RX path amplifier 2212 may amplify the RF signalsreceived by the antenna 2202.

An output of the RX path amplifier 2212 may be coupled to an input ofthe RX path pre-mix filter 2214, which may be a harmonic or band-pass(e.g., low-pass) filter, configured to filter received RF signals thathave been amplified by the RX path amplifier 2212.

An output of the RX path pre-mix filter 2214 may be coupled to an inputof the RX path mixer 2216, also referred to as a downconverter. The RXpath mixer 2216 may include two inputs and one output. A first input maybe configured to receive the RX signals, which may be current signals,indicative of the signals received by the antenna 2202 (e.g., the firstinput may receive the output of the RX path pre-mix filter 2214). Asecond input may be configured to receive local oscillator signals fromone of the local oscillators 2206. The RX path mixer 2216 may then mixthe signals received at its two inputs to generate a downconverted RXsignal, provided at an output of the RX path mixer 2216. As used herein,downconversion refers to a process of mixing a received RF signal with alocal oscillator signal to generate a signal of a lower frequency. Inparticular, the RX path mixer (e.g., downconverter) 2216 may beconfigured to generate the sum and/or the difference frequency at theoutput port when two input frequencies are provided at the two inputports. In some embodiments, the RF device 2200 may implement adirect-conversion receiver (DCR), also known as homodyne, synchrodyne,or zero-IF receiver, in which case the RX path mixer 2216 may beconfigured to demodulate the incoming radio signals using localoscillator signals whose frequency is identical to, or very close to thecarrier frequency of the radio signal. In other embodiments, the RFdevice 2200 may make use of downconversion to an intermediate frequency(IF). IFs may be used in superheterodyne radio receivers, in which areceived RF signal is shifted to an IF before the final detection of theinformation in the received signal is done. Conversion to an IF may beuseful for several reasons. For example, when several stages of filtersare used, they can all be set to a fixed frequency, which makes themeasier to build and to tune. In some embodiments, the RX path mixer 2216may include several such stages of IF conversion.

Although a single RX path mixer 2216 is shown in the RX path of FIG. 6 ,in some embodiments, the RX path mixer 2216 may be implemented as aquadrature downconverter, in which case it would include a first RX pathmixer and a second RX path mixer. The first RX path mixer may beconfigured for performing downconversion to generate an in-phase (I)downconverted RX signal by mixing the RX signal received by the antenna2202 and an in-phase component of the local oscillator signal providedby the local oscillator 2206. The second RX path mixer may be configuredfor performing downconversion to generate a quadrature (Q) downconvertedRX signal by mixing the RX signal received by the antenna 2202 and aquadrature component of the local oscillator signal provided by thelocal oscillator 2206 (the quadrature component is a component that isoffset, in phase, from the in-phase component of the local oscillatorsignal by 90 degrees). The output of the first RX path mixer may beprovided to a I-signal path, and the output of the second RX path mixermay be provided to a Q-signal path, which may be substantially 90degrees out of phase with the I-signal path.

The output of the RX path mixer 2216 may, optionally, be coupled to theRX path post-mix filter 2218, which may be low-pass filters. In case theRX path mixer 2216 is a quadrature mixer that implements the first andsecond mixers as described above, the in-phase and quadrature componentsprovided at the outputs of the first and second mixers respectively maybe coupled to respective individual first and second RX path post-mixfilters included in the filter 2218.

The ADC 2220 may be configured to convert the mixed RX signals from theRX path mixer 2216 from analog to digital domain. The ADC 2220 may be aquadrature ADC that, like the RX path quadrature mixer 2216, may includetwo ADCs, configured to digitize the downconverted RX path signalsseparated in in-phase and quadrature components. The output of the ADC2220 may be provided to the digital processing unit 2208, configured toperform various functions related to digital processing of the RXsignals so that information encoded in the RX signals can be extracted.

Turning to the details of the TX path that may be included in the RFdevice 2200, the digital signal to later be transmitted (TX signal) bythe antenna 2202 may be provided, from the digital processing unit 2208,to the DAC 2230. Like the ADC 2220, the DAC 2230 may include two DACs,configured to convert, respectively, digital I- and Q-path TX signalcomponents to analog form.

Optionally, the output of the DAC 2230 may be coupled to the TX pathpre-mix filter 2228, which may be a band-pass (e.g., low-pass) filter(or a pair of band-pass, e.g., low-pass, filters, in case of quadratureprocessing) configured to filter out, from the analog TX signals outputby the DAC 2230, the signal components outside of the desired band. Thedigital TX signals may then be provided to the TX path mixer 2226, whichmay also be referred to as an upconverter. Like the RX path mixer 2216,the TX path mixer 2226 may include a pair of TX path mixers, forin-phase and quadrature component mixing. Like the first and second RXpath mixers that may be included in the RX path, each of the TX pathmixers of the TX path mixer 2226 may include two inputs and one output.A first input may receive the TX signal components, converted to theanalog form by the respective DAC 2230, which are to be upconverted togenerate RF signals to be transmitted. The first TX path mixer maygenerate an in-phase (I) upconverted signal by mixing the TX signalcomponent converted to analog form by the DAC 2230 with the in-phasecomponent of the TX path local oscillator signal provided from the localoscillator 2206 (in various embodiments, the local oscillator 2206 mayinclude a plurality of different local oscillators, or be configured toprovide different local oscillator frequencies for the mixer 2216 in theRX path and the mixer 2226 in the TX path). The second TX path mixer maygenerate a quadrature phase (Q) upconverted signal by mixing the TXsignal component converted to analog form by the DAC 2230 with thequadrature component of the TX path local oscillator signal. The outputof the second TX path mixer may be added to the output of the first TXpath mixer to create a real RF signal. A second input of each of the TXpath mixers may be coupled the local oscillator 2206.

Optionally, the RF device 2200 may include the TX path post-mix filter2224, configured to filter the output of the TX path mixer 2226.

The TX path amplifier 2222 may include an array of PAs, e.g., an arrayof PAs similar to the PAs 430, and may be implemented together with anyof the DPD arrangements described herein, where DPD using a multi-modeDPD capture circuit may be used to provide predistorted input signals tothe TX path amplifier 2222.

In various embodiments, any of the RX path pre-mix filter 2214, the RXpath post-mix filter 2218, the TX post-mix filter 2224, and the TXpre-mix filter 2228 may be implemented as RF filters. In someembodiments, an RF filter may be implemented as a plurality of RFfilters, or a filter bank. A filter bank may include a plurality of RFfilters that may be coupled to a switch, e. g., the RF switch 2234,configured to selectively switch any one of the plurality of RF filterson and off (e.g., activate any one of the plurality of RF filters), inorder to achieve desired filtering characteristics of the filter bank(i.e., in order to program the filter bank). For example, such a filterbank may be used to switch between different RF frequency ranges whenthe RF device 2200 is, or is included in, a BS or in a UE device. Inanother example, such a filter bank may be programmable to suppress TXleakage on the different duplex distances.

The impedance tuner 2232 may include any suitable circuitry, configuredto match the input and output impedances of the different RF circuitriesto minimize signal losses in the RF device 2200. For example, theimpedance tuner 2232 may include an antenna impedance tuner. Being ableto tune the impedance of the antenna 2202 may be particularlyadvantageous because antenna’s impedance is a function of theenvironment that the RF device 2200 is in, e.g., antenna’s impedancechanges depending on, e.g., if the antenna is held in a hand, placed ona car roof, etc.

As described above, the RF switch 2234 may be a device configured toroute high-frequency signals through transmission paths, e.g., in orderto selectively switch between a plurality of instances of any one of thecomponents shown in FIG. 6 , e.g., to achieve desired behavior andcharacteristics of the RF device 2200. For example, in some embodiments,an RF switch may be used to switch between different antennas 2202. Inother embodiments, an RF switch may be used to switch between aplurality of RF filters (e.g., by selectively switching RF filters onand off) of the RF device 2200. Typically, an RF system would include aplurality of such RF switches.

The RF device 2200 provides a simplified version and, in furtherembodiments, other components not specifically shown in FIG. 6 may beincluded. For example, the RX path of the RF device 2200 may include acurrent-to-voltage amplifier between the RX path mixer 2216 and the ADC2220, which may be configured to amplify and convert the downconvertedsignals to voltage signals. In another example, the RX path of the RFdevice 2200 may include a balun transformer for generating balancedsignals. In yet another example, the RF device 2200 may further includea clock generator, which may, e.g., include a suitable phased-lock loop(PLL), configured to receive a reference clock signal and use it togenerate a different clock signal that may then be used for timing theoperation of the ADC 2220, the DAC 2230, and/or that may also be used bythe local oscillator 2206 to generate the local oscillator signals to beused in the RX path or the TX path.

Example Data Processing System

FIG. 7 provides a block diagram illustrating an example data processingsystem 2300 that may be configured to control operation of one or moreDPD arrangements as described herein, according to some embodiments ofthe present disclosure. For example, the data processing system 2300 maybe configured to implement or control portions of performing DPD using amulti-mode DPD capture circuit as described with reference to FIGS. 1-6, in particular to implement or control portions of DPD arrangements asillustrated in FIGS. 4-5 , or any further embodiments of the DPDarrangements as described herein. In another example, the dataprocessing system 2300 may be configured to implement at least portionsof the control logic 2236, shown in FIG. 6 .

As shown in FIG. 7 , the data processing system 2300 may include atleast one processor 2302, e.g., a hardware processor 2302, coupled tomemory elements 2304 through a system bus 2306. As such, the dataprocessing system may store program code within memory elements 2304.Further, the processor 2302 may execute the program code accessed fromthe memory elements 2304 via a system bus 2306. In one aspect, the dataprocessing system may be implemented as a computer that is suitable forstoring and/or executing program code. It should be appreciated,however, that the data processing system 2300 may be implemented in theform of any system including a processor and a memory that is capable ofperforming the functions described within this disclosure.

In some embodiments, the processor 2302 can execute software or analgorithm to perform the activities as discussed in the presentdisclosure, in particular activities related to performing DPD using amulti-mode DPD capture circuit as described herein. The processor 2302may include any combination of hardware, software, or firmware providingprogrammable logic, including by way of non-limiting example amicroprocessor, a digital signal processor (DSP), a field-programmablegate array (FPGA), a programmable logic array (PLA), an applicationspecific integrated circuit (IC) (ASIC), or a virtual machine processor.The processor 2302 may be communicatively coupled to the memory element2304, for example in a DMA configuration, so that the processor 2302 mayread from or write to the memory elements 2304.

In general, the memory elements 2304 may include any suitable volatileor non-volatile memory technology, including double data rate (DDR) RAM,synchronous RAM (SRAM), dynamic RAM (DRAM), flash, read-only memory(ROM), optical media, virtual memory regions, magnetic or tape memory,or any other suitable technology. Unless specified otherwise, any of thememory elements discussed herein should be construed as beingencompassed within the broad term “memory.” The information beingmeasured, processed, tracked or sent to or from any of the components ofthe data processing system 2300 could be provided in any database,register, control list, cache, or storage structure, all of which can bereferenced at any suitable timeframe. Any such storage options may beincluded within the broad term “memory” as used herein. Similarly, anyof the potential processing elements, modules, and machines describedherein should be construed as being encompassed within the broad term“processor.” Each of the elements shown in the present figures, e.g.,any elements illustrating DPD arrangements for performing DPD using amulti-mode DPD capture circuit as shown in FIGS. 1-6 , can also includesuitable interfaces for receiving, transmitting, and/or otherwisecommunicating data or information in a network environment so that theycan communicate with, e.g., the data processing system 2300.

In certain example implementations, mechanisms performing DPD using amulti-mode DPD capture circuit as outlined herein may be implemented bylogic encoded in one or more tangible media, which may be inclusive ofnon-transitory media, e.g., embedded logic provided in an ASIC, in DSPinstructions, software (potentially inclusive of object code and sourcecode) to be executed by a processor, or other similar machine, etc. Insome of these instances, memory elements, such as e.g. the memoryelements 2304 shown in FIG. 7 , can store data or information used forthe operations described herein. This includes the memory elements beingable to store software, logic, code, or processor instructions that areexecuted to carry out the activities described herein. A processor canexecute any type of instructions associated with the data or informationto achieve the operations detailed herein. In one example, theprocessors, such as e.g. the processor 2302 shown in FIG. 7 , couldtransform an element or an article (e.g., data) from one state or thingto another state or thing. In another example, the activities outlinedherein may be implemented with fixed logic or programmable logic (e.g.,software/computer instructions executed by a processor) and the elementsidentified herein could be some type of a programmable processor,programmable digital logic (e.g., an FPGA, a DSP, an erasableprogrammable read-only memory (EPROM), an electrically erasableprogrammable read-only memory (EEPROM)) or an ASIC that includes digitallogic, software, code, electronic instructions, or any suitablecombination thereof.

The memory elements 2304 may include one or more physical memory devicessuch as, for example, local memory 2308 and one or more bulk storagedevices 2310. The local memory may refer to RAM or other non-persistentmemory device(s) generally used during actual execution of the programcode. A bulk storage device may be implemented as a hard drive or otherpersistent data storage device. The processing system 2300 may alsoinclude one or more cache memories (not shown) that provide temporarystorage of at least some program code in order to reduce the number oftimes program code must be retrieved from the bulk storage device 2310during execution.

As shown in FIG. 7 , the memory elements 2304 may store an application2318. In various embodiments, the application 2318 may be stored in thelocal memory 2308, the one or more bulk storage devices 2310, or apartfrom the local memory and the bulk storage devices. It should beappreciated that the data processing system 2300 may further execute anoperating system (not shown in FIG. 7 ) that can facilitate execution ofthe application 2318. The application 2318, being implemented in theform of executable program code, can be executed by the data processingsystem 2300, e.g., by the processor 2302. Responsive to executing theapplication, the data processing system 2300 may be configured toperform one or more operations or method steps described herein.

Input/output (I/O) devices depicted as an input device 2312 and anoutput device 2314, optionally, can be coupled to the data processingsystem. Examples of input devices may include, but are not limited to, akeyboard, a pointing device such as a mouse, or the like. Examples ofoutput devices may include, but are not limited to, a monitor or adisplay, speakers, or the like. In some embodiments, the output device2314 may be any type of screen display, such as plasma display, liquidcrystal display (LCD), organic light emitting diode (OLED) display,electroluminescent (EL) display, or any other indicator, such as a dial,barometer, or LEDs. In some implementations, the system may include adriver (not shown) for the output device 2314. Input and/or outputdevices 2312, 2314 may be coupled to the data processing system eitherdirectly or through intervening I/O controllers.

In an embodiment, the input and the output devices may be implemented asa combined input/output device (illustrated in FIG. 7 with a dashed linesurrounding the input device 2312 and the output device 2314). Anexample of such a combined device is a touch sensitive display, alsosometimes referred to as a “touch screen display” or simply “touchscreen”. In such an embodiment, input to the device may be provided by amovement of a physical object, such as e.g. a stylus or a finger of auser, on or near the touch screen display.

A network adapter 2316 may also, optionally, be coupled to the dataprocessing system to enable it to become coupled to other systems,computer systems, remote network devices, and/or remote storage devicesthrough intervening private or public networks. The network adapter maycomprise a data receiver for receiving data that is transmitted by saidsystems, devices and/or networks to the data processing system 2300, anda data transmitter for transmitting data from the data processing system2300 to said systems, devices and/or networks. Modems, cable modems, andEthernet cards are examples of different types of network adapter thatmay be used with the data processing system 2300.

Example DPD Capture Circuit

FIG. 8 is a block diagram illustrating an example DPD capture circuit800, according to some embodiments of the present disclosure. The DPDcapture circuit 800 may be a hardware unit. In some aspects, the DPDcapture circuit 800 may be a digital hardware unit (e.g., includinggates, arithmetic logic, hardware state machine, etc.). In someinstances, the DPD capture circuit 800 may be integrated as part of anintegrated circuit device. In some instances, the DPD capture circuit800 may be implemented on a FPGA. The DPD capture circuit 800 can beimplemented by a communication system such as the communication systems400 and/or 500 and/or a RF device such as the RF device 2200. In someaspects, the DPD capture circuit 800 may correspond to the multi-modeDPD capture circuit 416 discussed above with reference to FIGS. 4 and/or5 . That is, the DPD capture circuit 800 can be implemented as part ofthe DPD circuit 410.

The DPD capture circuit 800 can capture data for estimating or updatingDPD coefficients. As explained above, data can be captured at variousdata points associated with a DPD for updating DPD coefficients. Forinstance, the signals 802 may be a feedback signal (e.g., the feedbacksignal 431) associated with a nonlinear component (e.g., the PA 430)having a nonlinear distortion in which the DPD is configured topre-compensate. Further, the DPD capture circuit 800 may capture DPDrelated data from multiple channels corresponding to different datapoints of a transmit or receive path or of different transmit/receivedata paths. In some aspects, the DPD capture circuit 800 may implementmultiple configurable modes for capturing feedback signals from a PA(e.g., the PA 430). The multiple capturing modes may include anysuitable combinations of mode 1 to mode 5 as discussed above withreference to FIG. 5 . As shown, the DPD capture circuit 800 may includea measurement circuit 820, a capture triggering circuit 810, and one ormore capture buffers 830 similar to the capture buffers 502.

The capture triggering circuit 810 may generate triggers for capturingDPD related signals 802 based on a specified capture cycle timing. Insome aspects, the capture triggering circuit 810 may trigger capturingof multiple bursts of a DPD signal 802 (e.g., for mode 4) based on aspecified capture cycle timing. That is, the capture cycle timing can beprogrammable. As explained above, the capture cycle timing may specify anumber of consecutive data samples or signal samples to capture for eachburst. The capture cycle timing may also specify a spacing between thebursts and/or a number of bursts to capture. Such burst captures (spacedapart in time) may have different frequency and/or power content,enabling the DPD capture circuit 800 to assemble a more fullyrepresentative data sample. The multiple bursts (the trial captures) maybe used for determining statistics of expected captures in the nearfuture, and the determined statistics are then used to set thresholdsfor finding subsequent captures that meet the thresholds.

For instance, the measurement circuit 820 may compute the statisticsfrom the multiple bursts. The statistics can be related to at least oneof a peak power or a mean power. In some aspects, the measurementcircuit 820 may include an instantaneous power circuit to compute aninstantaneous power of the acquired trial captures and/or a peaklocation circuit to identify the highest peak in the instantaneous powersignal for each of the trial captures. In some aspects, the thresholdsfor finding a subsequent capture of the signal 802 may include an upperbound threshold peak power, a lower bound threshold peak power, an upperbound threshold mean power, a lower bound threshold mean power, an upperbound threshold number of samples exceeding a threshold, a lower boundthreshold number of samples exceeding a threshold or any combinationthereof.

In some aspects, the DPD capture circuit 800 may not store the multiplebursts (the trial capture) in the capture buffers 830 (e.g., local RAMsof the DPD capture circuit 800). In other words, the measurement circuit820 may perform measurements on the multiple bursts in real-time withoutstoring the multiple bursts in the capture buffers 830. Afterdetermining the one or more thresholds, the DPD capture circuit 800 maymonitor the DPD signal 802 for a subsequent portion of the DPD signal802 that satisfies the one or more threshold. Stated differently, theDPD capture circuit 800 may monitor the DPD signal 802 until a portionof the DPD signal 802 satisfies the one or more thresholds. Upondetecting the portion of the DPD signal 802 satisfying the one or morethresholds, the DPD capture circuit 800 may stop the monitoring andstore the portion of the DPD signal 802 in the capture buffers 830(e.g., a non-trial capture). That is, the DPD capture circuit 800 mayperform “a stop on pass capture” according to the one or morethresholds. Further, in some instances, the DPD capture circuit 800 maystore the portion of the DPD signal 802 satisfying the one or morethresholds to a main system memory (e.g., the memory 2308). Thetransferring of the captured portion of the DPD signal 802 from thecapture buffers 830 to the memory can be performed via a DMA engine. Insome instances, each capture buffer 830 may be attached to a respectiveDMA engine.

Subsequently, the portion of the DPD signal 802 satisfying the one ormore thresholds can be used for DPD coefficient update. Because of thedynamic nature of the DPD signal 802, utilizing multiple bursts (trialcaptures) to obtain statistics for setting thresholds for a non-trialcapture can advantageously allow capturing of a useful portion of theDPD signal 802 for DPD coefficient update. The useful portion may referto a portion of the DPD signal 802 that is most representative of DPDerrors or DPD behaviors. As such, DPD coefficients may converge to asuitable DPD solution or DPD model faster and/or more accurately, thusthe DPD may operate more effectively (to precompensate for nonlineardistortion).

Example DPD Data Capture Method for DPD Adaptation

FIG. 9 is a flow diagram of an example method 900 for capturing data forDPD adaptation, according to some embodiments of the present disclosure.The method 900 can be implemented by the communication systems 400and/or 500, the DPD data capture circuit 800, and/or the RF device 2200or any suitable wireless devices or RF transceivers. Although theoperations of the method 900 may be illustrated with reference toparticular embodiments of the communication system 400 and/or 500 and/orthe DPD capture circuit 800 disclosed herein, the method 900 may beperformed using any suitable hardware components and/or softwarecomponents. Operations are illustrated once each and in a particularorder in FIG. 9 , but the operations may be performed in parallel,reordered, and/or repeated as desired.

At 902, at least a portion of an input signal (e.g., x_(n) in FIG. 4and/or FIG. 5 ) is predistorted, using a DPD actuator circuit, based onDPD coefficients associated with a characteristic of a nonlinearcomponent. In some aspects, the DPD actuator circuit may correspond tothe DPD actuator 412 discussed above with reference to FIGS. 4 and/or 5. In some aspects, the nonlinear component may be a power amplifiersimilar to the power amplifier 430.

At 904, multiple portions (or multiple bursts) of a feedback signal(e.g., the feedback signal 431 z_(n) in FIG. 4 and/or FIG. 5 ) arecaptured based on a specified capture cycle timing using a DPD capturecircuit, where the feedback signal is indicative of an output of thenonlinear component. In some aspects, the DPD capture circuit maycorrespond to the multi-mode DPD capture circuit 416 discussed abovewith reference to FIGS. 4 and/or 5 and/or the DPD data capture circuit800 discussed above with reference to FIG. 8 . In some aspects, themultiple portions may correspond to multiple bursts acquired from thetrial captures discussed above with reference to FIGS. 5 and/or 8 . Insome aspects, the specified capture cycle timing may indicate a numberof consecutive samples to be captured for each burst, a spacing (intime) between each burst capture, and/or a number of bursts to capture.

At 906, one or more criteria for a subsequent capture of the feedbacksignal are computed based on one or more statistical measures of themultiple captured portions of the feedback signal.

At 908, the subsequent capture is performed based on the one or morecriteria. In some aspects, performing the subsequent capture may includemonitoring the feedback signal until a detection of a subsequent portionof the feedback signal satisfies the one or more criteria. In someaspects, the subsequent capture may correspond to a non-trial capture asdiscussed above with reference to FIGS. 5 and/or 8 .

At 910, the DPD coefficients is updated, using a DPD adaptation circuit,based at least in part on the subsequent portion of the feedback signal.In some aspects, the DPD adaptation circuit may correspond to the DPDadaptation circuit 414 discussed above with reference to FIGS. 4 and/or5 .

In some aspects, the method 900 may further include computing the one ormore statistical measures for the multiple portions of the feedbacksignal, where the one or more statistical measures are associated withat least one of a peak power or a mean power. In some aspects, computingthe one or more criteria for monitoring the feedback signal may includecomputing at least one of an upper bound threshold peak power, a lowerbound threshold peak power, an upper bound threshold mean power, a lowerbound threshold mean power, an upper bound threshold number of samplesexceeding a threshold, and/or a lower bound threshold number of samplesexceeding a threshold. Accordingly, performing the subsequent capture at908 may include monitoring the feedback signal to find a subsequentportion of the feedback signal (for adapting the DPD coefficients) thatsatisfies one or more of these thresholds or a combination of two ormore of these thresholds. As an example, the monitoring may include amean power threshold comparison (e.g., comparing a mean power of theportion to the upper bound threshold mean power and/or the lower boundthreshold mean power) and a peak power threshold comparison (e.g.,comparing a peak power of the portion to the upper bound threshold peakpower and/or the lower bound threshold peak power). As another example,the monitoring may include a mean power threshold comparison (e.g.,comparing a mean power of the portion to the upper bound threshold meanpower and/or the lower bound threshold mean power) and a number ofsamples comparison (e.g., comparing a number of samples in the portionexceeding a certain threshold to the upper bound threshold number ofsamples exceeding the certain threshold and/or the lower bound thresholdnumber of samples exceeding the certain threshold). As a furtherexample, the monitoring may include a peak power threshold comparison(e.g., comparing a peak power of the portion to the upper boundthreshold peak power and/or the lower bound threshold peak power) and anumber of samples comparison (e.g., comparing a number of samples in theportion exceeding a certain threshold to the upper bound thresholdnumber of samples exceeding the certain threshold and/or the lower boundthreshold number of samples exceeding the certain threshold). Ingeneral, the criteria or thresholds for finding a subsequent portion ofthe feedback signal (for adapting the DPD coefficients) may beassociated with a mean power, a peak power, and/or a number of samplesexceeding a certain threshold.

In some aspects, the method 900 may further include triggering thecapturing of the multiple portions of the feedback signal responsive toa register value (e.g., a register-write operation).

In some aspects, the method 900 may further include storing, at a memory(e.g., the memory 2308), the subsequent portion of the feedback signalbased the subsequent portion of the feedback signal satisfying the oneor more criteria. In some aspects, the method 900 may further includerefraining from storing, at the memory, the multiple portions of thefeedback signal captured for computing the one or more statisticalmeasures.

EXAMPLES

Example 1 includes a digital predistortion (DPD) arrangement. The DPDarrangement includes a DPD actuator circuit, configured to use DPDcoefficients (θ) to perform a predistortion of an input signal (x) togenerate a predistorted signal (u); a DPD adaptation circuit, configuredto update the DPD coefficients (θ) based on a model of a power amplifier(PA); and a multi-mode DPD capture circuit, configured to acquire one ormore captures of a feedback signal, the feedback signal indicative of anoutput of the PA, where the one or more captures are to be used toupdate the model of the PA, wherein the multi-mode DPD capture circuitis configured to operate in one of a plurality of modes.

In Example 2, the DPD arrangement according to Example 1 can optionallyinclude wherein the plurality of modes includes a mode where themulti-mode DPD capture circuit places a peak sample power of a capturewindow in a center of a capture buffer.

In Example 3, the DPD arrangement according to Examples 1 or 2 canoptionally include wherein the plurality of modes includes a mode wherethe multi-mode DPD capture circuit synchronizes the peak window startwith a frame at a programmed offset.

In Example 4, the DPD arrangement according to any one of Examples 1-3can optionally include wherein the plurality of modes includes a modewhere the multi-mode DPD capture circuit decimates data prior to storingthe one or more captures in one or more capture buffers.

In Example 5, the DPD arrangement according to any one of Examples 1-4can optionally include wherein the plurality of modes include a modewhere the multi-mode DPD capture circuit performs multiple capturecycles to compute one or more characteristics of data and set one ormore thresholds for subsequent captures.

In Example 6, the DPD arrangement according to any one of Examples 1-5,wherein the plurality of modes includes a mode where the multi-mode DPDcapture circuit accumulates samples over multiple captures.

Example 7 includes an RF device, e.g., an RF transceiver or a portionthereof, that includes a PA and a DPD arrangement according to any oneof the Examples 1-6.

In Example 8, the RF device according to Example 7 can optionallyinclude at least one antenna.

In Example 9, the RF device according to Examples 7 or 8 can optionallyinclude a control logic configured to control operation of the DPDarrangement.

In Example 10, the RF device according to any one of Examples 7-9 canoptionally include wherein the RF device is a mobile device (e.g., a UEof a wireless cellular network).

In Example 11, the RF device according to any one of Examples 7-9 canoptionally include wherein the RF device is a BS of a wireless cellularnetwork or a transmitter of a cable communications network.

Example 12 includes a non-transitory computer-readable storage medium,storing computer-readable instructions which, when executed by aprocessor, are configured to control operation of the DPD arrangement oran RF device according to any one of Examples 1-11.

Example 13 includes a digital predistortion (DPD) arrangement. The DPDarrangement includes a DPD actuator circuit to predistort, using DPDcoefficients, at least a portion of an input signal, the DPDcoefficients associated with a characteristic of a nonlinear component;a DPD capture circuit to perform, based on a capture cycle timing,multiple captures of a feedback signal, the feedback signal indicativeof an output of the nonlinear component; compute, based on one or morecharacteristics of the multiple captures, one or more criteria for asubsequent capture of the feedback signal; and perform, based on the oneor more criteria, the subsequent capture of the feedback signal; and aDPD adaptation circuit to update the DPD coefficients based at least inpart on the subsequent capture.

In Example 14, the DPD arrangement according to Example 13 canoptionally include where the DPD capture circuit further computes theone or more characteristics for the multiple captures.

In Example 15, the DPD arrangement according to any of Examples 13-14can optionally include where the one or more characteristics of themultiple captures includes a statistical measure associated with atleast one of a peak power or a mean power.

In Example 16, the DPD arrangement according to any of Examples 13-15can optionally include where the DPD capture circuit further stores, ata memory, the statistical measure associated with the at least one ofthe peak power or the mean power.

In Example 17, the DPD arrangement according to any of Examples 13-16can optionally include where the DPD capture circuit computes the one ormore criteria by setting one or more thresholds for the subsequentcapture based on the one or more characteristic for the multiplecaptures.

In Example 18, the DPD arrangement according to any of Examples 13-17can optionally include where the one or more thresholds for thesubsequent capture includes at least one of an upper bound thresholdpeak power; a lower bound threshold peak power; an upper bound thresholdmean power; a lower bound threshold mean power; an upper bound thresholdnumber of samples exceeding a first threshold; or a lower boundthreshold number of samples exceeding a second threshold.

In Example 19, the DPD arrangement according to any of Examples 13-18can optionally include where the DPD capture circuit performs thesubsequent capture based on the one or more criteria by monitoring thefeedback signal until a portion of the feedback signal satisfies the oneor more criteria.

In Example 20, the DPD arrangement according to any of Examples 13-19can optionally include where the DPD adaptation circuit updates the DPDcoefficients further based on the portion of the feedback signal thatsatisfies the one or more criteria.

In Example 21, the DPD arrangement according to any of Examples 13-20can optionally include where the DPD capture circuit further stops thesubsequent capture based on a detection of the portion of the feedbacksignal satisfying the one or more criteria.

In Example 22, the DPD arrangement according to any of Examples 13-21can optionally include where the DPD capture circuit further stores, ata memory, the portion of the feedback signal satisfying the one or morecriteria.

Example 23 includes a radio frequency (RF) device including a nonlinearcomponent; a digital predistortion (DPD) actuator circuit to predistort,using DPD coefficients, at least a portion of an input signal, the DPDcoefficients associated with a characteristic of the nonlinearcomponent; a DPD capture circuit to capture, based on a specifiedcapture cycle timing, multiple bursts of a feedback signal, the feedbacksignal indicative of an output of the nonlinear component; compute,based on the multiple bursts, one or more statistical measures fordetermining one or more thresholds for a subsequent capture; and performthe subsequent capture by monitoring the feedback signal for asubsequent portion of the feedback signal that satisfies the one or morethresholds; and a DPD adaptation circuit to update the DPD coefficientsbased at least in part on the subsequent portion of the feedback signalthat satisfies the one or more thresholds.

In Example 24, the RF device according to Example 23 can optionallyinclude where the DPD capture circuit further determines, based on theone or more computed statistical measures of the multiple bursts of thefeedback signal, the one or more thresholds for the subsequent captureof the feedback signal.

In Example 25, the RF device according to any of Examples 23-24 canoptionally include where the one or more thresholds for the subsequentcapture of the feedback signal includes at least one of an upper boundthreshold peak power; a lower bound threshold peak power; an upper boundthreshold mean power; a lower bound threshold mean power; an upper boundthreshold number of samples exceeding a first threshold; or a lowerbound threshold number of samples exceeding a second threshold.

In Example 26, the RF device according to any of Examples 23-25 canoptionally include where the DPD capture circuit includes a capturetriggering circuit to trigger, based on the specified capture cycletiming, capturing of the multiple bursts of the feedback signal; and ameasurement circuit to compute, based on the multiple bursts, the one ormore statistical measures for determining the one or more thresholds forthe subsequent capture.

Example 27 includes a method for performing digital predistortion (DPD),the method including predistorting, using a DPD actuator circuit, atleast a portion of an input signal based on DPD coefficients associatedwith a characteristic of a nonlinear component; capturing, based on aspecified capture cycle timing using a DPD capture circuit, multipleportions of a feedback signal, the feedback signal indicative of anoutput of the nonlinear component; computing, based on one or morestatistical measures of the multiple captured portions of the feedbacksignal, one or more criteria for a subsequent capture of the feedbacksignal; performing the subsequent capture based on the one or morecriteria, where the performing includes monitoring the feedback signaluntil a detection of a subsequent portion of the feedback signalsatisfies the one or more criteria; and updating, using a DPD adaptationcircuit, the DPD coefficients based at least in part on the subsequentportion of the feedback signal.

In Example 28, the method according to Example 27 can optionally includecomputing the one or more statistical measures for the multiple portionsof the feedback signal, where the one or more statistical measures areassociated with at least one of a peak power or a mean power.

In Example 29, the method according to any of Examples 27-28 canoptionally include where the computing the one or more criteria formonitoring the feedback signal includes computing at least one of anupper bound threshold peak power; a lower bound threshold peak power; anupper bound threshold mean power; a lower bound threshold mean power; anupper bound threshold number of samples exceeding a threshold; or alower bound threshold number of samples exceeding a threshold.

In Example 30, the method according to any of Examples 27-29 canoptionally include triggering the capturing of the multiple portions ofthe feedback signal responsive to a register value.

In Example 31, the method according to any of Examples 27-30 canoptionally include storing, at a memory, the subsequent portion of thefeedback signal based the subsequent portion of the feedback signalsatisfying the one or more criteria.

In Example 32, the method according to any of Examples 27-31 canoptionally include refraining from storing, at a memory, the multipleportions of the feedback signal captured for computing the one or morestatistical measures.

Variations and Implementations

While embodiments of the present disclosure were described above withreferences to exemplary implementations as shown in FIGS. 1-9 , a personskilled in the art will realize that the various teachings describedabove are applicable to a large variety of other implementations. Forexample, descriptions provided herein are applicable not only to 5Gsystems, which provide one example of wireless communication systems,but also to other wireless communication systems such as, but notlimited to, Wi-Fi technology or Bluetooth technology. In yet anotherexample, descriptions provided herein are applicable not only towireless communication systems, but also to any other systems whereamplifiers may be used, such as radar systems, automotive radar, andcable communication systems (e.g., cable television systems, etc.).

In certain contexts, the features discussed herein can be applicable toautomotive systems, medical systems, scientific instrumentation,wireless and wired communications, radio, radar, anddigital-processing-based systems.

In the discussions of the embodiments above, components of a system,such as phase shifters, frequency mixers, transistors, resistors,capacitors, amplifiers, and/or other components can readily be replaced,substituted, or otherwise modified in order to accommodate particularcircuitry needs. Moreover, it should be noted that the use ofcomplementary electronic devices, hardware, software, etc., offer anequally viable option for implementing the teachings of the presentdisclosure related to performing DPD using a multi-mode DPD capturecircuit as described herein.

Parts of various systems for performing DPD using a multi-mode DPDcapture circuit, as proposed herein, can include electronic circuitry toperform the functions described herein. In some cases, one or more partsof the system can be provided by a processor specially configured forcarrying out the functions described herein. For instance, the processormay include one or more application specific components, or may includeprogrammable logic gates which are configured to carry out the functionsdescribe herein. The circuitry can operate in analog domain, digitaldomain, or in a mixed-signal domain. In some instances, the processormay be configured to carrying out the functions described herein byexecuting one or more instructions stored on a non-transitorycomputer-readable storage medium.

In one example embodiment, any number of electrical circuits of thepresent drawings may be implemented on a board of an associatedelectronic device. The board can be a general circuit board that canhold various components of the internal electronic system of theelectronic device and, further, provide connectors for otherperipherals. More specifically, the board can provide the electricalconnections by which the other components of the system can communicateelectrically. Any suitable processors (inclusive of DSPs,microprocessors, supporting chipsets, etc.), computer-readablenon-transitory memory elements, etc. can be suitably coupled to theboard based on particular configuration needs, processing demands,computer designs, etc. Other components such as external storage,additional sensors, controllers for audio/video display, and peripheraldevices may be attached to the board as plug-in cards, via cables, orintegrated into the board itself. In various embodiments, thefunctionalities described herein may be implemented in emulation form assoftware or firmware running within one or more configurable (e.g.,programmable) elements arranged in a structure that supports thesefunctions. The software or firmware providing the emulation may beprovided on non-transitory computer-readable storage medium comprisinginstructions to allow a processor to carry out those functionalities.

In another example embodiment, the electrical circuits of the presentdrawings may be implemented as stand-alone modules (e.g., a device withassociated components and circuitry configured to perform a specificapplication or function) or implemented as plug-in modules intoapplication specific hardware of electronic devices. Note thatparticular embodiments of the present disclosure may be readily includedin a SOC package, either in part, or in whole. An SOC represents an ICthat integrates components of a computer or other electronic system intoa single chip. It may contain digital, analog, mixed-signal, and oftenRF functions: all of which may be provided on a single chip substrate.Other embodiments may include a multi-chip-module (MCM), with aplurality of separate ICs located within a single electronic package andconfigured to interact closely with each other through the electronicpackage.

It is also imperative to note that all of the specifications,dimensions, and relationships outlined herein (e.g., the number ofcomponents shown in the systems of FIGS. 1-9 ) have only been offeredfor purposes of example and teaching only. Such information may bevaried considerably without departing from the spirit of the presentdisclosure, or the scope of the appended claims. It should beappreciated that the system can be consolidated in any suitable manner.Along similar design alternatives, any of the illustrated circuits,components, modules, and elements of the present drawings may becombined in various possible configurations, all of which are clearlywithin the broad scope of this specification. In the foregoingdescription, example embodiments have been described with reference toparticular processor and/or component arrangements. Variousmodifications and changes may be made to such embodiments withoutdeparting from the scope of the appended claims. The description anddrawings are, accordingly, to be regarded in an illustrative rather thanin a restrictive sense.

It is also important to note that the functions related to performingDPD using a multi-mode DPD capture circuit as proposed herein illustrateonly some of the possible functions that may be executed by, or within,RF systems. Some of these operations may be deleted or removed whereappropriate, or these operations may be modified or changed considerablywithout departing from the scope of the present disclosure. Substantialflexibility is provided by embodiments described herein in that anysuitable arrangements, chronologies, configurations, and timingmechanisms may be provided without departing from the teachings of thepresent disclosure.

What is claimed is:
 1. A digital predistortion (DPD) system withmulti-mode capture, the DPD system comprising: a DPD actuator circuit topredistort at least a portion of an input signal using DPD coefficients,the DPD coefficients associated with a nonlinear component; a multi-modeDPD capture circuit to acquire one or more captures of a feedbacksignal, the multi-mode DPD capture circuit operable in a plurality ofmodes, and the feedback signal indicative of an output signal of thenonlinear component; and a DPD adaptation circuit to update the DPDcoefficients based at least in part on the one or more captures.
 2. TheDPD system of claim 1, wherein the DPD adaptation circuit is to combinecaptures from at least two different modes of the plurality of modes. 3.The DPD system of claim 1, wherein the plurality of modes comprises amode where the multi-mode DPD capture circuit places a peak sample powerof a capture window substantially in a center of a capture buffer. 4.The DPD system of claim 3, wherein the plurality of modes comprisesanother mode where the multi-mode DPD capture circuit synchronizes apeak window start with a frame at a programmed offset, and a capture iscentered at the peak sample power that is within the peak window.
 5. TheDPD system of claim 3, wherein the plurality of modes comprises anothermode where the multi-mode DPD capture circuit decimates data prior tostoring the one or more captures.
 6. The DPD system of claim 3, whereinthe plurality of modes comprises another mode where the multi-mode DPDcapture circuit accumulates samples over multiple captures to performaveraging.
 7. The DPD system of claim 1, wherein the plurality of modescomprises a mode where the multi-mode DPD capture circuit synchronizes apeak window start with a frame at a programmed offset.
 8. The DPD systemof claim 7, wherein the plurality of modes comprises another mode wherethe multi-mode DPD capture circuit decimates data prior to storing theone or more captures.
 9. The DPD system of claim 1, wherein theplurality of modes comprises a mode where the multi-mode DPD capturecircuit decimates data prior to storing the one or more captures in oneor more capture buffers.
 10. The DPD system of claim 1, wherein theplurality of modes comprises a mode where the multi-mode DPD capturecircuit accumulates samples over multiple captures to perform averaging.11. The DPD system of claim 1, wherein the plurality of modes comprisesat least two of: a first mode where the multi-mode DPD capture circuitplaces a peak sample power of a capture window substantially in a centerof a capture buffer; a second mode where the multi-mode DPD capturecircuit synchronizes a peak window start with a frame at a programmedoffset; a third mode where the multi-mode DPD capture circuit decimatesdata prior to storing the one or more captures; a fourth mode where themulti-mode DPD capture circuit performs multiple capture cycles tocompute one or more characteristics of data and set one or morethresholds for subsequent captures; or a fifth mode where the multi-modeDPD capture circuit accumulates samples over multiple captures toperform averaging.
 12. A radio frequency (RF) device comprising: anonlinear component; a digital predistortion (DPD) actuator circuit topredistort at least a portion of an input signal using DPD coefficients,the DPD coefficients associated with the nonlinear component; amulti-mode DPD capture circuit to acquire captures of a feedback signalassociated with at least two different modes of a plurality of modes,and the feedback signal indicative of an output signal of the nonlinearcomponent; and a DPD adaptation circuit to update the DPD coefficientsbased at least in part on the captures.
 13. The RF device of claim 12,wherein the plurality of modes comprises at least two of: a first modewhere the multi-mode DPD capture circuit places a peak sample power of acapture window substantially in a center of a capture buffer; a secondmode where the multi-mode DPD capture circuit synchronizes a peak windowstart with a frame at a programmed offset; a third mode where themulti-mode DPD capture circuit decimates data prior to storing thecaptures; a fourth mode where the multi-mode DPD capture circuit wherethe multi-mode DPD capture circuit performs multiple capture cycles tocompute one or more characteristics of data and set one or morethresholds for subsequent captures; or a fifth mode where the multi-modeDPD capture circuit accumulates samples over multiple captures toperform averaging.
 14. The RF device of claim 12, wherein the nonlinearcomponent comprises a power amplifier.
 15. The RF device of claim 12,wherein the RF device is a mobile device.
 16. The RF device of claim 12,wherein the RF device is a base station.
 17. A method of digitalpredistortion (DPD) with multi-mode capture, the method comprising:capturing, using a multi-mode DPD capture circuit, a feedback signal ina first mode, the feedback signal indicative of an output of a nonlinearcomponent; capturing, using the multi-mode DPD capture circuit, thefeedback signal in a second mode, the second mode being different thanthe first mode; updating, using a DPD adaptation circuit, DPDcoefficients associated with the nonlinear component based at least inpart on the capturing the feedback signal in the first mode and thecapturing the feedback signal in the second mode; and predistorting,using a DPD actuator circuit, at least a portion of an input signalbased on the DPD coefficients from the updating.
 18. The method of claim17, wherein the multi-mode DPD capture circuit places a peak samplepower of a capture window substantially in a center of a capture bufferin the first mode.
 19. The method of claim 18, wherein the multi-modeDPD capture circuit synchronizes a peak window start with a frame at aprogrammed offset in the second mode.
 20. The method of claim 18,wherein the multi-mode DPD capture circuit accumulates samples overmultiple captures to perform averaging in the second mode.